Solar Collector

ABSTRACT

The invention is a solar powered heat exchanger ( 10 ) comprising a solar collector ( 12 ), a heat accumulator ( 14 ), and a heat exchanger ( 16 ). The solar collector is operatively coupled to the heat accumulator ( 14 ) via a supply line ( 18 ) and a recirculation line ( 20 ). The heat accumulator ( 14 ) is in turn operatively coupled to the heat exchanger ( 16 ) via a feed line ( 22 ) and a return line ( 24 ).

FIELD OF THE INVENTION

The present invention relates broadly to a solar collector and a solarpowered heat exchanger. The invention also relates to a solar trackingapparatus and a combination solar collector/tracking apparatus.

BACKGROUND OF THE INVENTION

Solar hot water systems of a conventional construction include a solarcollector connected to a storage cylinder containing stored water. Thesolar collector is fabricated from an arrangement of heat absorbingpipes or tubes layed out in a parallel or serpentine arrangement. In oneform the tubes are formed in a black heat absorbing mat which can beplaced on a rooftop to capture the sunlight. In another form the pipesare housed within an enclosure having a glass pane front which isexposed to sunlight and the efficiency of heating is improved under theinfluence of the greenhouse effect. The system may provide directheating where the stored water itself is circulated through the solarcollector. Alternatively, indirect heating may be provided where forexample a glycol mixture is recirculated through the solar collector andan associated solar circuit which passes through the storage cylinder.The storage cylinder includes a heat exchanger for indirect heating ofthe stored water utilising the heat of the glycol mixture in the solarcircuit. In either case of direct or indirect heating, the stored wateror glycol mixture is pumped through the solar collector until thetemperature of the stored water is equal to or approaches that of theliquid in the solar collector.

Conventional solar collectors absorb short wave radiation which istransferred by conduction into the fluid being heated. As the fluidtemperature rises so does the temperature of the collector surface. Heatenergy is lost from the collector by re-radiation from the heatedcollector surface in the form of long wave radiation, and the higher thecollector surface temperature the more heat energy is re-radiated (orlost) from the collector. Because of this effect, efficiency ofconventional collectors declines rapidly as the temperature of theheated fluid rises until eventually the long wave radiation losses fromthe collector surface equal the short wave radiation being absorbed bythe collector and no further heating can occur. The maximum fluidtemperature that can be achieved with conventional collectors is about85 to 90 deg C.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided asolar collector comprising:

a collector housing having a translucent or transparent surface andbeing sealed to permit at least partial evacuation or reduction inpressure within the housing below atmospheric pressure; anda collector tank located within the collector housing and having a solarabsorbent surface located adjacent the translucent or transparentsurface, the collector tank being adapted to contain a heat transferfluid which, on exposure of the solar collector to sunlight, is heatedvia solar energy which penetrates the translucent or transparent surfaceand, with the increased efficiency provided by the sealed and at leastpartially evacuated housing, is absorbed onto the solar absorbentsurface which transfers heat to the heat transfer fluid.

Preferably the sealed collector housing defines a chamber between atleast the translucent or transparent surface and the absorbent surfaceof the collector tank. More preferably the housing includes anevacuation valve which permits evacuation of the sealed chamber fordrawing at least a partial vacuum within the chamber. Even morepreferably the sealed chamber surrounds the collector tank which isseparated from the collector housing on opposing internal surfaces byflexible spacers.

Preferably the solar collector includes an adjustable mounting assemblyto which the collector housing is mounted, the mounting assembly beingadapted to provide reorientation of the solar collector to increaseexposure of the absorbent surface to sunlight. More preferably theadjustable mounting assembly effects seasonal reorientation of the solarcollector by rotation about a first axis. Even more preferably theadjustable mounting assembly is effective in tracking the sun bypivoting about a second axis arranged generally transverse to the firstaxis. Still more preferably the first axis is the altitude axis and thesecond axis the azimuth axis.

According to another aspect of the invention there is provided a solarpowered heat exchanger comprising:

a solar collector including a collector housing having a translucent ortransparent surface, the collector housing being sealed to permit atleast partial evacuation or reduction in pressure within the housingbelow atmospheric pressures and a collector tank located within thecollector housing and being adapted to contain a heat transfer fluid;a heat accumulator operatively coupled to the solar collector forstoring the heat transfer fluid heated by exposure of the solarcollector to sunlight wherein solar energy penetrates the translucent ortransparent surface and, with the increased efficiency provided by thesealed and at least partially evacuated housing, is absorbed onto thesolar absorbent surface which transfers heat to the heat transfer fluid;anda heat exchanger operatively coupled to the heat accumulator and beingarranged for transferring heat to an external device utilising the heatof the heat transfer fluid from the heat accumulator or the solarcollector.

Preferably the heat exchanger includes a heat exchange chamber in heatexchange communication with the external device, the heat exchangechamber being connected to the heat accumulator via a feed line whichprovides the heat transfer fluid from the accumulator. More preferablythe heat exchange chamber is also connected to the accumulator via areturn line for returning the heat transfer fluid to the accumulatorafter said fluid has exchanged its heat with the external device. Evenmore preferably the heat exchanger also includes an expansion tankconnected to the heat exchange chamber and being designed to allow theheated fluid to expand as its temperature rises thus maintaining arelatively constant and low hydrostatic pressure within the heatexchanger. Still more preferably the heat exchanger further includes apump connected to the return line to promote flow of the heat transferfluid from the heat exchange chamber to the heat accumulator.

Preferably the heat accumulator includes an accumulator chimneyconnected to a supply line connected to the outlet of the collectortank, the accumulator chimney being positioned within the accumulator toconvey the heat transfer fluid from the outlet of the collector tank.Additionally, the heat exchanger includes a heat exchange chimneyconnected to the feed line which interconnects the heat accumulator andthe heat exchanger, the heat exchange chimney being positioned withinthe heat exchange chamber to convey the heat transfer fluid from theheat accumulator.

Preferably the solar powered heat exchanger also comprises arecirculation line connected between the heat accumulator and the solarcollector for recirculation of the heat transfer fluid. More preferablythe collector tank includes an inlet connected to the recirculationline, and an outlet coupled to the heat accumulator, the outlet beingelevated relative to the inlet to effect a flow of the heat transferfluid from the inlet to the outlet and recirculation of the heattransfer fluid through the recirculation line by a thermal siphon effectat the inlet. Even more preferably the collector tank includes aplurality of internal baffle plates being arranged to support the tankand oriented to promote the flow of the heat transfer fluid from theinlet to the outlet.

Preferably the solar powered heat exchanger further comprises atemperature control system operatively coupled to the heat exchanger tocontrol the flow of the heat transfer fluid to the heat exchanger andthus the amount of heat exchanged with the external device. Morepreferably the temperature control system includes a control valveconnected to the feed line, and a temperature sensor connected to theexternal device, the temperature sensor being operatively coupled to thecontrol valve whereby, depending on the temperature of the externaldevice, the control valve is throttled to control the flow of the heattransfer fluid to the heat exchanger.

Preferably the heat transfer fluid is a liquid such as glycol or awater/glycol mixture.

Accordingly to a further aspect of the invention there is provided asolar tracking apparatus comprising:

a base being adapted to mount to a solar collector;a shading member connected to the base at a fixed and predeterminedangle;a pair of light sensitive elements mounted on the base on respectiveopposing sides of the shading member; andan actuator operatively coupled to the pair of light sensitive elementswhereby in operation the light sensitive elements, dependent of theirrelative exposure to sunlight as controlled by the shading member, drivethe actuator to effect movement of the solar collector.

Preferably the base is planar and the shading member is fixedsubstantially perpendicular to the planar base. More preferably theshading member includes a generally straight lower portion fixed to thebase, and an upper portion extending from the lower portion at an obtuseangle. Even more preferably the upper portion includes a reflectivesurface on its lower face and directed toward one of the light sensitiveelements.

Preferably, the light sensitive elements are each in the form of a lightdependent resistor. Preferably the solar tracking apparatus alsocomprises an actuator circuit including the light dependent resistorswhich dependent on their exposure to sunlight are configured to drivethe actuator. More preferably the actuator circuit includes a voltagecomparator having voltage inputs from the light dependent resistors anda reference voltage, respectively, whereby differential voltage appliedto the inputs of the voltage comparator causes it to conduct driving theactuator. Even more preferably all output of the voltage comparator isconnected to a transistor which is electrically coupled to and actuatesa relay whereby the application of differential voltage to thecomparator causes the comparator and the transistor to conduct and closethe relay which in turn powers the actuator. Still more preferably therelay includes an electromagnetic relay connected to a normally-openrelay contact.

Preferably the actuator is in the form of a drive motor. More preferablythe drive motor is electrically coupled to the pair of light sensitiveelements via the actuator circuit.

According to yet another aspect of the invention there is provided acombination of a solar collector and a solar tracking apparatus asdisclosed in the preceding aspects, the tracking apparatus beingconnected to the solar collector and designed for reorientation of thecollector to optimise its exposure to sunlight.

Preferably the solar tracking apparatus is arranged to rotate the solarcollector about an azimuth axis to effectively track the sun andoptimise daily exposure to sunlight. More preferably the trackingapparatus is one of a pair of said apparatuses, the other solar trackingapparatus being designed to permit rotation or tilting of the solarcollector about an altitude axis to optimise its seasonal exposure tosunlight.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to achieve a better understanding of the nature of the presentinvention a preferred embodiment of a solar collector, solar poweredheat exchanger, and solar tracking apparatus will now be described, byway of example only, with reference to the accompanying drawings inwhich:

FIG. 1 is a schematic illustration of a solar powered heat exchanger ofan embodiment of one aspect of the invention;

FIG. 2 is a sectional view taken through A-A of the solar collector ofFIG. 1;

FIG. 3 is another sectional view taken through B-B of the accumulatorand heat exchanger of FIG. 1; and

FIG. 4 is a further sectional view taken through C-C of the heatexchanger of FIG. 3;

FIG. 5 is a plan and elevational view of the solar powered heatexchanger of FIG. 1 together with an adjustable mounting assembly;

FIG. 6 is a side elevational view of a solar powered heat exchangertogether with a solar tracking apparatus of an embodiment of a furtheraspect of the invention;

FIG. 7 is a plan and elevational view of a tracker sensor of the solartracking apparatus of FIG. 6;

FIG. 8 is a circuit diagram of the solar tracking apparatus of FIG. 6;and

FIG. 9 is a schematic illustration of the tracker sensor showing itsrotational movement about the azimuth axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1 there is a solar powered heat exchanger designatedgenerally as 10 comprising a solar collector 12, a heat accumulator 14,and a heat exchanger 16. The solar collector 12 is operatively coupledto the heat accumulator 14 via a supply line 18 and a recirculation line20. The heat accumulator 14 is in turn operatively coupled to the heatexchanger 16 via a feed line 22 and a return line 24.

The solar collector 12 includes a collector housing 26 having atranslucent or transparent surface in the form of a glass pane 28. Thesolar collector 12 also includes a collector tank 30 located within thecollector housing 26 and in operation being adapted to contain a heattransfer fluid such as glycol or a water/glycol mixture. Thewater/glycol mixture is heated by the solar collector 12 and circulatesby a thermosiphon effect between the solar collector 12 and the heataccumulator 14 via the supply and the recirculation lines 18 and 20,respectively. The solar heated water/glycol mixture flows from the heataccumulator 14 to the heat exchange 16 via the feed line 22 andtransfers heat to an external device 32 which is in heat communicationwith the heat exchanger 16. The water/glycol mixture is then returned tothe heat accumulator 14 via the return line 24 either by pump ofthermosiphon.

As best shown in FIG. 2, the solar collector 12 is of a generally flatand cuboidal configuration wherein the collector housing 26 includes arectangular perimeter frame 34 sandwiched between a rear opaque plate 36and the front glass pane 28. The glass pane 28 and the rear plate 36 arefixed to the perimeter frame 34 via a sealant 38. This arrangementprovides a sealed chamber 40 within the collector housing 26 which isspecifically designed to permit a reduction in pressure within thehousing below atmospheric pressure, or preferably a full vacuum. Thecollector tank 30 includes a solar absorbent surface 41 which faces theglass pane 28 for exposure to sunlight, and is shaped and coloured(preferably matt black) for maximum solar absorption.

It is understood that by evacuating the sealed chamber 40 between thesolar absorbent surface 41 and the translucent covering or glass pane28, radiation losses from the absorbent surface 41 (which are long wave)are reduced or eliminated because heat transfer by convection away fromthe solar absorbent surface 41 to the exterior is eliminated and longwave radiation cannot travel through the glass pane 28. Therefore theefficiency of the evacuated/sealed chamber 40 is fairly uniformregardless of fluid temperature, and much higher temperatures can beachieved.

The sealed collector housing 26 houses the collector tank 30 which is ofa complementary shape to the sealed pressure reduction chamber 40. Thesealed chamber 40 surrounds all faces of the collector tank 30 which isspaced from the glass pane 28 and the rear plate 36 by respectiveinternal flexible spacers such as 42 and 44. The collector tank 30 hasan inlet 46 and an outlet 48 diagonally spaced and located in oppositeperimeter walls and connected to the recirculation line 20 and thesupply line 18, respectively. The collector tank 30 also includes aseries of internal baffle plates such as 50 which in this example areequally spaced transversally and arranged generally parallel to oneanother. The solar collector 12 is oriented so that the collector tankoutlet 48 is elevated relative to its inlet 46 to provide a flow of thewater/glycol mixture through the collector tank 30 with a thermal siphoneffect at the inlet 46. The internal baffle plates such as 50 are, asbest shown in FIG. 1, oriented relative to the inlet 46 and outlet 48 tofurther promote this flow of the heat transfer fluid.

The solar collector 12 is designed to permit at least partial evacuationof the sealed chamber 40 about the collector tank 30. The collectorhousing 26 or perimeter frame 34 of this embodiment includes anevacuation valve 51 which permits evacuation of the sealed chamber 40for drawing a vacuum within the chamber 40. The flexible spacers such as42 and 44 maintain the separation between the collector housing 26 andthe collector tank 30 whereas the baffle plates such as 50 providesupport for the relatively thin walled collector tank 30. The supply andrecirculation lines 18 and 20 pass through insulating glands such as 52located within openings in the perimeter frame 34 aligned with the tankinlet and outlet 46 and 48. This arrangement allows the collector tank30 to expand or contract relative to the collector housing 26 underdifferential temperature conditions.

As shown in FIG. 3, the heat accumulator 14 includes a cylindricalaccumulator tank 54 laid on its side, and an accumulator chimney 56extending radially across the tank 54 from its circumferential wall. Theaccumulator chimney 56 is connected to the supply line 18 and isdisposed in a generally upright position. The accumulator chimney 56 isin this disposition designed to allow the heated fluid to rise byconvection from the collector 12 into the top of the accumulator 14. Thechimney 56 is insulated to reduce heat transfer from the rising heatedfluid to cooler fluid stored in the accumulator 14. The accumulator tank54 is of a size and volume dependent on the heating requirements. Forexample, if heating is required for extended periods outside effectivesunlight hours then the accumulator tank 54 will be relatively large.The accumulator tank 54 is insulated with known cladding (not shown) tominimise heat losses from the heat transfer fluid. The recirculationline 20 extends within the accumulator tank 54 with its mouth orentrance 58 at a height dependent on the maximum volume of heat transferfluid to be retained in the heat accumulator 14. The feed line 22 isconnected to the accumulator tank 54 and generally aligned coaxiallywith the accumulator chimney 56. The feed line 22 is flared outwardly ina frusto-conical form 60 at its connection to the accumulator tank 54.It is understood that this flared connection immediately adjacent theaccumulator tank 56 increases the rate at which the heat transfer fluidor water/glycol mixture can flow into the heat accumulator 14.

The heat exchanger 16 of this embodiment includes a heat exchangechamber 62 within which the heat exchange device 32 is partly housed.The heat exchanger 16 also includes a heat exchange chimney 64 connectedto the feed line 22 and arranged upright within the heat exchangechamber 62 to allow hot fluid to rise to the top of the exchanger 16.The feed line 22 includes a control valve in the form of a throttlevalve 66 for controlling the flow of the water/glycol mixture to theheat exchanger 16 depending on the heating requirements of the externaldevice 32. The heat exchanger 16 is also provided with a temperaturesensor 68 operatively coupled to the external device 32 and designed,dependent on the external device 32 temperature, to control throttlingof the control valve 66. The heat exchanger 16 further includes anexpansion tank 70 connected to the heat exchange chamber 62 via arelatively small pipe 72 and designed to allow for expansion of the heattransfer fluid within the heat exchanger 16. The expansion tank 70 has aloose fitting lid to allow atmosphere to leave or enter the tank 70according to the level of fluid in the tank 70. The water/glycol mixturehaving exchanged its heat within the heat exchanger 16 is returned tothe heat accumulator 14 via the return line 24. The return line 24 ofthis example includes a pump 76 designed to promote the flow of heattransfer fluid from the heat exchanger 16 to the heat accumulator 14.Alternatively, a thermosiphon effect may eliminate the need for a pump.

FIG. 4 shows in cross section the external device 32 with which thesolar powered heat exchanger 10 of this embodiment exchanges heat. Theexternal device 32 includes another chamber 76 which contains a separatefluid to be heated. Heat transfer fluid in the heat exchange chamber 62transfers heat by conduction through the walls of the other chamber 32into the separate fluid to be heated. As the transfer fluid cools itfalls by thermosiphon to the bottom of the heat exchange chamber 62 andthen flows via the return line 24 back to the accumulator 14.

In order to further facilitate an understanding of this embodiment ofthe solar powered heat exchanger 10, the general steps involved in itsoperation are as follows:

-   1. solar energy is absorbed by the solar collector 12 which    effectively heats the heat transfer fluid or the water/glycol    mixture;-   2. the water/glycol mixture is caused to flow into the collector    tank 30 of the solar collector 12 and rises upwardly through the    accumulator chimney 56;-   3. depending on the load and heating requirements, the solar heated    water/glycol mixture rises into the heat exchanger 16 via the heat    exchange chimney 64 at a volume/flow rate dictated by the control    valve 66;-   4. as the relatively hot heat transfer fluid enters the top of the    accumulator 14, cooler fluid retained in the accumulator 14 falls by    thermosiphon towards the bottom of the accumulator 14 and by    thermosiphon returns via the recirculation line 20 to the bottom of    the collector 12;-   5. the water/glycol mixture rising into the heat exchange chamber 62    of the heat exchanger 16 exchanges heat with, and effectively heats,    the external device 32; and-   6. the heat depleted water/glycol mixture is returned to the heat    accumulator 14 via the return line 24 under the assistance of the    pump or by a thermosiphon action.

As shown in FIG. 5, and in order to increase the exposure of the solarcollector 12 to sunlight, the solar collector 12 includes an adjustablemounting assembly 90 to which the collector housing 26 is mounted. Theadjustable mounting assembly 90 includes a mechanical actuator and lockarrangement 92 having a lever 94 at one end being fixed to a shaft 96,and releasably lockable to a fixed seasonal reference point. The level94 includes a retractable pin (not shown) which in this example engagesone of three (3) holes 100A to C in the plate 98 which are angularlydisplaced depending on the season, summer, spring/autumn, and winterrespectively. The mounting assembly 90 also includes a drive motor 102connected to a drive shaft or spindle 104 which in turn is fixed to thesolar collector 12. The drive motor 102 thus rotates the solar collector12 to track the sun and maximise daily exposure to sunlight.

The adjustable mounting assembly 90 is thus effective in providingeither continuous or intermittent seasonal reorientation of the solarcollector 12 by re-inclination or orientation about a primary oraltitude axis. The adjustable mounting assembly 90 may also permitpivoting about a secondary or azimuth axis, arranged generallytransverse to the primary axis, and designed to have the solar collector12 effectively track the sun during daylight hours.

FIG. 6 illustrates a variant of the solar powered heat exchanger of FIG.1 together with an embodiment of a solar tracking apparatus 110 of afurther aspect of the invention. The solar tracking apparatus 110 ofthis embodiment is one of a pair of these apparatuses 110 and 110′ beingdesigned for rotation of the solar collector 12′ about an azimuth axis112 and an altitude axis 114, respectively.

The solar collector 12′ (preferably together with the accumulator andheat exchange not shown) is elevated above ground via a fixed supportcolumn or pedestal 116. The pedestal 116 is at an upper end rotationallymounted to an intermediate mounting assembly 118 for tilting orreinclination of the solar collector 12′ about the altitude axis 114.The intermediate mounting assembly 118 provides mounting for a drivemotor 120 having a shaft 122 defining the azimuth axis 112 about whichthe solar collector 12 is rotated. The shaft 122 is rotatable about theintermediate support assembly 118 and fixed to a mounting bracket 124which in turn is secured to an underlying surface of the solar collector12′.

The solar tracking apparatus 110 for rotation of the solar collector 12′about the azimuth axis 112 includes the drive motor 120 together with anazimuth sensor 126. The other solar tracking apparatus 110′ includes analtitude drive motor 128 having a shaft fixed to the intermediatemounting assembly 118 for tilting of the solar collector 12′ about thealtitude axis 114, and an altitude sensor 130. The azimuth and altitudesensors 126 and 130 are mounted coplanar with and at opposing sides ofthe solar collector 12′ facing the sun.

FIG. 7 shows in elevation and plan the tracker sensors 126 and 130 ofthe apparatus of FIG. 6. The azimuth sensor 126 for example includes abase plate 132 to which a generally upright shading member or arm 134 isfixed at right angles. The shading arm 134 is at its upper end formedcontinuous with a reflector 136 ranged at an obtuse angle to the shadingarm 134. Importantly, the tracker sensor 126 includes a pair of lightsensitive elements in the form of light dependent resistors (LDR) 138and 140 mounted to an upper face of the base plate 132 on opposing sidesof the shading arm 134. The shading arm 134 together with the reflector136 control the relative exposure of the opposing LDRs 138 and 140 tosunlight.

In order to better understand the solar tracking apparatus, itsoperation will now be described with reference to FIGS. 8 and 9.

The opposing LDRs 138 and 140 are as the name suggests light dependentand have a relatively high electrical resistance in low and zero light,and relatively low resistance in bright light. Therefore, with referenceto the actuator circuit 150 of FIG. 8, with equal intensity of lightfalling on both LDRs 138/140 (normal condition) the voltage at V1 ishalf the supply voltage. If the intensity of light on LDR1 138 risesabove that on LDR2 140 then the voltage at the one rises above half thesupply voltage. Conversely, if the intensity of light on LDR1 138 fallsbelow that on LDR2 140 then the voltage at Vl falls below half thesupply voltage.

The actuator circuit 150 of the embodiment includes a voltage dividerprovided by resistors R1 152 and R2 154 which provides a referencevoltage at V2 equal to half the supply voltage. The circuit 150 alsoincludes a voltage comparator A1 or 156 having positive and negativeinputs to which the respective voltages V1 and V2 are applied. Thecircuit 150 further includes another voltage comparator 158 havingpositive and negative inputs to which the respective voltages V2 and V1are also applied.

In operation and with equal light falling on both LDRs 138/140 neitherof the voltage comparators 156 or 158 conduct. With increased light on,for example, LDR1 138 an output of the comparator A1 or 156 isrelatively high whereas an output of the other voltage comparator A or158 remains relatively low. The voltage comparator A1 or 156 iselectrically connected to a transistor Q1 or 160 which under theseconditions is caused to conduct which in turn energises anelectromagnetic relay R1 or 162 to which it is connected. The energisedrelay R1 or 162 causes associated relay contacts CR1 or 164 to close andapply a normal voltage polarity to the actuator or, for example, azimuthdrive motor 120.

If on the other hand LDR2 or 140 is exposed to increased light thiscauses the output of the voltage comparator A2 or 158 to be relativelyhigh whilst the voltage output of the other comparator A1 or 156 remainsrelatively low. Under these conditions, another transistor Q2 or 166which is connected to the output of the comparator A2 or 158 conducts toenergise an electromagnetic relay R or 168. The energised relay 168closes relay contacts 170 which apply a reversed voltage polarity to thedrive motor 120.

As schematically illustrated in FIG. 9, the tracker sensor 126 of thisexample 130 provides effective rotation of the solar collector about theazimuth axis 112 to maximise its daily exposure to sunlight. With equallight falling on LDR1 or 138 and LDR2 or 140 the drive motor 120 for theazimuth rotation is not energised. If light falling on the LDR1 or 138is higher in intensity than that falling on the LDR2 or 140 then thedrive motor 120 rotates in one direction or vice versa.

As shown in FIG. 9 the solar tracking apparatus rotates the solarcollector about the azimuth axis 112 in the following stages:

-   1. with the sun vertically above the plane of the base 132 and the    collector, both of the LDRs 138/140 receive equal light intensity    and the azimuth drive motor 120 is off;-   2. as the sun moves towards the west the reflector 136 shades the    LDR2 or 140 which now receives less light than the LDR1 or 138 and    the drive motor is energised and the associated solar collector    rotated about its azimuth axis 112;-   3. the shadow cast by the reflector 136 leaves the LDR2 140 and both    LDRs 138/140 receive equal light and the motor is de-energised so    that the solar collector is directly facing the sun; and-   4. at sunset the solar collector panel is facing west and the solar    collector remains stationary overnight until the sun rises the next    morning and light from the eastern horizon is reflected by the    reflector 136 onto the LDR2 or 140 which receives a higher light    intensity than the LDR1 or 138 and the drive motor is energised in    the opposite direction to rotate the solar collector on its azimuth    axis 112 until the solar collector is facing the sun and the LDRs    138/140 are receiving equal light intensity.

It will be appreciated that tracking of the sun during daylight hours isthen continued or repeated as outlined in stages 1-3 above. Thesensitivity of the solar tracking apparatus can be adjusted by theheight of the shading arm such as 134 whereby increasing its heightincreases the apparent speed with which the shadow of the shading arm134 falls on the LDR or 140. It will also be appreciated that the othersolar tracking apparatus 110′ of FIG. 6 operates in a similar mannerwherein the altitude drive motor 128 rotates or tilts the solarcollector 12′ about its altitude axis 114. The altitude sensor 130 isgenerally oriented perpendicular to the azimuth sensor 126 in that ithas its shading arm disposed in an east-west direction so as to maintainthe solar collector 12′ facing the track of the sun as its altitudevaries between summer and winter.

The solar powered heat exchanger 10 of this embodiment has applicationin the heating of water where, for example, the external device 32contains a domestic potable water supply. In another application, thesolar powered heat exchanger 10 is used as a heat source for driving anapparatus designed to produce water from ambient air. The specificationof the applicant's Australian provisional application No. 2003904488describes an apparatus of this type, and the disclosure of thisspecification is included herein by way of reference. In yet anotherapplication, heat from the solar powered heat exchanger 10 may be usedin an absorption system to drive a refrigerator or an air-conditioner.

Now that a preferred embodiment of the present invention has beendescribed in some detail it will be apparent to those skilled in the artthat the solar collector, the solar powered heat exchanger, or the solartracking apparatus have the following advantages:

-   1. the solar collector, having a sealed collector housing within    which at least a partial vacuum can be drawn, provides efficient    absorption of solar energy for heating of the heat transfer fluid    and allows higher temperatures to be achieved;-   2. the configuration of the solar collector and orientation of its    inlet and outlet provides an effective flow of the heat transfer    fluid promoted by a thermosiphon effect at the inlet of the    collector tank;-   3. the solar powered heat exchanger utilises density differences in    the heat transfer fluid between the bottom of the collector (cooler    and higher density) and the top of the heat exchanger (hotter and    lower density) wherein the heat transfer fluid heated in the    collector becomes less dense and rises by natural convection forces    to the highest point of the heat exchange system whereas as the    fluid cools in the heat exchanger it becomes more dense and falls to    the bottom of the system; and-   4. the solar tracking apparatus is effective in tracking the sun    daily and/or seasonally to preferably provide maximum sunlight    exposure for the solar collector.

Those skilled in the art would appreciate that the invention describedherein is susceptible to variations and modifications other than thosespecifically described. For example, the specific construction of thesolar collector may vary from that described provided the heat transferfluid is effectively heated within the solar collector. The controlmechanisms by which the flow of heat transfer fluid is controlled to theheat exchanger may also vary. Likewise, the construction and control ofthe adjustable mounting assembly for the solar collector may bedifferent from that described.

All such variations and modifications are to be considered within thescope of the present invention and nature of which is to be determinedfrom the foregoing description.

1. A solar collector comprising: a collector housing having atranslucent or transparent surface and being sealed to permit at leastpartial evacuation or reduction in pressure within the housing belowatmospheric pressure; a collector tank located within the collectorhousing and having a solar absorbent surface located adjacent thetranslucent or transparent surface, the collector tank being adapted tocontain a heat transfer fluid which, on exposure of the solar collectorto sunlight, is heated via solar energy which penetrates the translucentor transparent surface and, with the increased efficiency provided bythe sealed and at least partially evacuated housing, is absorbed ontothe solar absorbent surface which transfers heat to the heat transferfluid; and an adjustable mounting assembly to which the collectorhousing is mounted, the mounting assembly being adapted to providereorientation of the solar collector to increase exposure of theabsorbent surface to sunlight.
 2. A solar collector as defined in claim1 wherein the sealed collector housing defines a chamber between atleast the translucent or transparent surface and the absorbent surfaceof either of the collector tank.
 3. A solar collector as defined inclaim 1 wherein either of the housing includes an evacuation valve whichpermits evacuation of the sealed chamber for drawing at least a partialvacuum within the chamber.
 4. A solar collector as defined in claim 1wherein the sealed chamber surrounds the collector tank which isseparated from the collector housing on opposing internal surfaces byflexible spacers.
 5. A solar collector as defined in claim 1 wherein theadjustable mounting assembly effects seasonal reorientation of the solarcollector by rotation about a first axis.
 6. A solar collector asdefined in claim 5 wherein the adjustable mounting assembly is effectivein tracking the sun by pivoting about a second axis arranged generallytransverse to the first axis.
 7. A solar collector as defined in claim 6wherein the first axis is the altitude axis and the second axis theazimuth axis.
 8. A solar collection as defined in claim 1 wherein theheat transfer fluid is a liquid including glycol or a water/glycolmixture.
 9. A solar powered heat exchanger comprising: a solar collectorincluding a collector housing having a translucent or transparentsurface, the collector housing being sealed to permit at least partialevacuation or reduction in pressure within the housing below atmosphericpressure, and a collector tank located within the collector housing andbeing adapted to contain a heat transfer fluid; a heat accumulatoroperatively coupled to the solar collector for storing the heat transferfluid heated by exposure of the solar collector to sunlight whereinsolar energy penetrates the translucent or transparent surface and, withthe increased efficiency provided by the sealed and at least partiallyevacuated housing, is absorbed onto the solar absorbent surface whichtransfers heat to the heat transfer fluid; and a heat exchangeroperatively coupled to the heat accumulator and being arranged fortransferring heat to an external device utilising the heat of the heattransfer fluid from the heat accumulator or the solar collector.
 10. Asolar powered heat exchanger as defined in claim 9 wherein the heatexchanger includes a heat exchange chamber in heat exchangecommunication with the external device, the heat exchanger chamber beingconnected to the heat accumulator via a feed line which provides theheat transfer from the accumulator.
 11. A solar powered heat exchangeras defined in claim 10 wherein the heat exchange chamber is connected tothe accumulator via a return line for returning the heat transfer fluidto the accumulator after said fluid has exchanged its heat with theexternal device.
 12. A solar heat powered heat exchanger as defined inclaim 10 wherein the heat exchanger also includes an expansion tankconnected to the heat exchange chamber and designed to allow the heatedfluid to expand as its temperature rises thus maintaining a relativelyconstant and low hydrostatic pressure within the heat exchanger.
 13. Asolar powered heat exchanger as defined in claim 11 wherein the heatexchanger further includes a pump connected to the return line topromote flow of the heat transfer fluid from the heat exchange chamberto the heat accumulator.
 14. A solar powered heat exchanger as definedin claim 10 wherein the heat exchanger includes a heat exchange chimneyconnected to a feed line which interconnects the heat accumulator andthe heat exchanger, the heat exchanger chimney being positioned withinthe heat exchange chamber to convey the heat transfer fluid from theheat accumulator.
 15. A solar powered heat exchanger as defined in claim9 wherein the heat accumulator includes an accumulator chimney connectedto a supply line connected to the outlet of the collector tank, theaccumulator chimney being positioned within the accumulator to conveythe heat transfer fluid from the outlet of the collector tank.
 16. Asolar powered heat exchanger as defined in claim 9 also comprising arecirculation line connected between the heat accumulator and the solarcollector for recirculation of the heat transfer fluid.
 17. A solarpowered heat exchanger as defined in claim 16 wherein the collector tankincludes an inlet connected to the recirculation line, and an outletcoupled to the heat accumulator, the outlet being elevated relative tothe inlet to effect a flow of the heat transfer fluid from the inlet tothe outlet and recirculation of the heat transfer fluid through therecirculation line by a thermalsiphon effect at the inlet.
 18. A solarpowered heat exchanger as defined in claim 17 wherein the collector tankincludes a plurality of internal baffle plates being arranged to supportthe tank and oriented to promote the flow of the heat transfer fluidfrom the inlet to the outlet.
 19. A solar powered heat exchanger asdefined in claim 9 further comprising a temperature control systemoperatively coupled to the heat exchanger to control the flow of theheat transfer fluid to the heat exchanger and thus the amount of heatexchanged with the external device.
 20. A solar powered heat exchangeras defined claim 19 wherein the temperature control system includes acontrol valve connected to the feed line, and a temperature sensorconnected to the external device, the temperature sensor beingoperatively coupled to the control valve whereby, depending on thetemperature of the external device, the control valve is throttled tocontrol the flow of the heat transfer fluid to the heat exchanger.
 21. Asolar powered heat exchanger as defined in claim 9 wherein the heattransfer fluid is a liquid such as glycol or a water/glycol mixture. 22.A solar tracking apparatus comprising: a base being adapted to mount toa solar collector; a shading member connected to the base at a fixed andpredetermined angle, the shading member including a generally straightlower portion fixed to the base, and an upper portion extending from thelower portion at an obtuse angle; a pair of light sensitive elementsmounted on the base on respective opposing sides of the shading member,the upper portion of said shading member including a reflective surfaceon its lower face and directed toward one of the light sensitiveelements; and an actuator operatively coupled to the pair of lightsensitive elements whereby in operation the light sensitive elements,dependent on their relative exposure to sunlight as controlled by theshading member, drive the actuator to effect movement of the solarcollector.
 23. A solar tracking apparatus as defined in claim 22 whereinthe base is planar and the shading member is fixed substantiallyperpendicular to the planar base.
 24. A solar tracking apparatus asdefined in claim 22, wherein the light sensitive elements are each inthe form of a light dependent resistor.
 25. A solar tracking apparatusas defined in claim 24, wherein the solar tracking apparatus alsocomprises an actuator circuit including the light dependent resistorswhich dependent on their exposure to sunlight are configured to drivethe actuator.
 26. A solar tracking apparatus as defined in claim 25,wherein the actuator circuit includes a voltage comparator havingvoltage inputs from the light dependent resistors and a referencevoltage, respectively, whereby differential voltage applied to theinputs of the voltage comparator causes it to conduct thereby drivingthe actuator.
 27. A solar tracking apparatus as defined in claim 26wherein an output of the voltage comparator is connected to a transistorwhich is electrically coupled to and actuates a relay whereby theapplication of differential voltage to the comparator causes thecomparator and the transistor to conduct and close the relay which inturn powers the actuator.
 28. A solar tracking apparatus as defined inclaim 27, wherein the relay includes an electromagnetic relay connectedto a normally-open relay contact.
 29. A solar tracking apparatustracking apparatus as defined in claim 25 wherein the actuator is in theform of a drive motor.
 30. A solar tracking apparatus as defined inclaim 29 wherein the drive motor is electrically coupled to the pair oflight sensitive elements via the actuator circuit. 31-36. (canceled) 37.The solar collector of claim 1 further comprising a solar trackingapparatus, the solar tracking apparatus being connected to the solarcollector and designed for reorientation of the collector to optimiseits exposure to sunlight wherein the solar tracking apparatus includes abase being adapted to mount to a solar collector; a shading memberconnected to the base at a fixed and predetermined angle, the shadingmember including a generally straight lower portion fixed to the base,and an upper portion extending from the lower portion at an obtuseangle; a pair of light sensitive elements mounted on the base onrespective opposing sides of the shading member, the upper portion ofsaid shading member including a reflective surface on its lower face anddirected toward one of the light sensitive elements; and an actuatoroperatively coupled to the pair of light sensitive elements whereby inoperation the light sensitive elements, dependent on their relativeexposure to sunlight as controlled by the shading member, drive theactuator to effect movement of the solar collector.
 38. The solarcollector of claim 37 wherein the solar tracking apparatus is arrangedto rotate the solar collector about an azimuth axis to effectively trackthe sun and optimise daily exposure to sunlight.
 39. The solar collectorof claim 38 further comprising an additional solar tracking apparatus,the additional solar tracking apparatus being designed to permitrotation or tilting of the solar collector about an altitude axis tooptimise its seasonal exposure to sunlight.